With some general science lessons and basic experiments, educators can teach middle school students about the differences between the concepts of mass and density. Once students are clear on how mass and density are used within the world of science, they can begin to expand and deepen their understanding of mechanics and physics.

Before discussing the differences between mass and density, students need to first understand each of the concepts separately. Mass is a measurement of the amount of matter in an object. Mass is an unchanging figure, regardless of the environment of the object. For example, a pumpkin with a mass of 5 kilograms maintains the same mass when placed underwater. While the different environments will make the pumpkin feel lighter underwater, it still weighs 5 kilograms.

Density is determined through the formula of mass divided by volume. As a physical property of matter, density demonstrates the amount of weight an object has for its size. While two objects may be the same size, their densities may be very different. For example, a 3-pound shot put and a large orange can be the same size but the fruit weighs less than the shot put, so it is less dense.

Teach kids the concept of mass by creating a classroom demonstration about the scientific principle. Gather objects that are drastically different in size and show them to your students. Instruct the kids to write down which of the objects they think have more mass. For example, show them a beach ball and a small paper weight. Allow a student to come to the front and pick up each object. While bigger, the beach ball will be considerably lighter and have less mass than the paper weight.

Show kids the physical presence of density with an in-class demonstration. Materials needed include two ice cube trays, sand, water and a large glass bowl. Freeze water in the ice cube tray. Fill the other ice cube tray with sand to simulate amounts of sand that are the same size as the ice cubes. Fill the large glass bowl with water. Ask two students to volunteer to come to the front of your classroom. Have the volunteers verify to the remaining students that the ice cubes and the sand cubes are the same size. Instruct them to pour both items into the glass bowl at the same time. The ice cubes will float and the sand will disperse and sink because it is denser than the ice cubes.